I agree with there being a margin of error or tolerance where the decision is umpire’s call. 100%. Both in recognition that the system cannot claim to be 100% accurate but also to keep the human element of the game.
However, for me, the issue with LBW is where to draw the line at the point that the ball hits the pad. To me it makes no sense to draw the line from the middle of the ball, it ought to be drawn from where the ball itself actually makes contact with the pad. That is where the ball has “hit” the batter, not a few centimetres to the left where the middle of the ball (which hasn’t hit the batter) is found.
By all means ensure that this line itself falls within the line drawn from the middle of off-stop to take it outside of the margin for umpire’s call but that is all the tolerance this needs for that aspect of lbw. Where the ball pitches is different, because the ball obviously lands on its middle so using the middle of the ball for that line is fine. That’s not the case with where the ball hits the pads. It is the “point of impact” that counts, not where the middle of the ball is at that point.
This is the lbw rule:
36.1 Out LBW
The striker is out LBW if all the circumstances set out in 36.1.1 to 36.1.5 apply.
36.1.1 The bowler delivers a ball, not being a No ball
36.1.2 the ball, if it is not intercepted full-pitch, pitches in line between wicket and wicket or on the off side of the striker’s wicket
36.1.3 the ball not having previously touched his/her bat, the striker intercepts the ball, either full-pitch or after pitching, with any part of his/her person
36.1.4 the point of impact, even if above the level of the bails,
either is between wicket and wicket
or if the striker has made no genuine attempt to play the ball with the bat, is between wicket and wicket or outside the line of the off stump.
36.1.5 but for the interception, the ball would have hit the wicket.
36.2 Interception of the ball
36.2.1 In assessing points in 36.1.3, 36.1.4 and 36.1.5, only the first interception is to be considered.
36.2.2 In assessing point 36.1.3, if the ball makes contact with the striker’s person and bat simultaneously, this shall be considered as the ball having first touched the bat.
36.2.3 In assessing point 36.1.5, it is to be assumed that the path of the ball before interception would have continued after interception, irrespective of whether the ball might have pitched subsequently or not.
36.3 Off side of wicket
The off side of the striker’s wicket shall be determined by the striker’s stance at the moment the ball comes into play for that delivery. See Appendix A.13.